Webgui unaccessible when port has a DHCP given address

[gdur]

Hi,
Today I ran into an unexpected problem while setting up a new server to replace old hardware.
After the initial install I was able to login while pointing to the LAN port with default given IP address as per default.
I created an 3rd port OPT1 and initially configured this port with DHCP. What ever rule I made for this OPT1 port I couldn't get access to the web interface. After some hair pulling hours the only difference I could find was that on my "old" OPNSense box the OPT1 port had a fixed IP address instead of DHCP. So I changed on my new box OPT1 to a fixed available IP address and voila, the https connection was established. Now I changed the fixed IP address to the same one given by DHCP and no connection is possible. Firewall log shows that the request may pass so ends up in the firewall itself with no response.
What is the explanation for this behavior? Is this a hidden feature?

[Patrick M. Hausen]

Did you change the "Listen Interface" for the web UI in any way?

[gdur]

Obviously I did, otherwise it also wouldn't work with a fixed IP address...

[Patrick M. Hausen]

Leave the listen interface at "All (recommended)" if you want to connect via a dynamically configured IF.

Otherwise the UI might be started before the interface is ready leading to the observed effects.

[gdur]

I left the listen interface at "All " so your answer is not a solution.

[Patrick M. Hausen]

You wrote that you had changed it "obviously" when I asked for that. If you didn't I am out of ideas for now.

[gdur]

Well actually I didn't changed it but I left it as was which is "All" by default. I appreciate your response though.